Contribution of E-selectin to cellular infiltration during endotoxin-induced uveitis

The selectin family is a group of early-reactive adhesion molecules that plays a role in the rolling phase of leukocytes in cellular infiltration. It has been reported that P-selectin is expressed on vascular endothelium in the iris-ciliary body 15 minutes after lipopolysaccharide (LPS) treatment in endotoxin-induced uveitis (EIU) and may contribute to the initial phase of ocular inflammation. The objective of the present study was to identify the expression pattern of E-selectin, another member of the selectin family, and to investigate the role of E-selectin during the course of EIU.

Endotoxin-induced uveitis was induced in male Lewis rats by a footpad injection of 200 microg LPS. The time-dependent expressions of E-selectin in EIU in the iris- ciliary body and the retina were studied by immunohistochemistry using wholemounts and paraffin-embedded sections and by monitoring the level of E-selectin mRNA expression. A monoclonal antibody to E-selectin and a control antibody were each injected intravenously to evaluate the effects of E-selectin inhibition on ocular inflammation at the time of maximum uveitis. In the anterior uvea, the effect was evaluated by the number of infiltrated cells and by the protein concentration in the aqueous humor 24 hours after LPS treatment; in the retina, the myeloperoxidase (MPO) activity was measured 48 hours after LPS treatment. The effect of the combined injection of anti-P-selectin and anti-E-selectin antibodies was also studied. It was then determined whether the delayed inhibition of E-selectin (6, 12, or 24 hours after LPS injection) could contribute to the early resolution of the uveitis.

E-selectin immunoreactivity was observed on the vessel walls of the iris and retina 7 hours after LPS treatment in wholemounts and paraffin-embedded sections and remained positive for 24 hours after LPS treatment. The expression of E-selectin messenger RNA gene peaked at 6 hours and again at 18 hours after LPS treatment in the iris- ciliary body and retina. The expression returned to the basal level 24 hours after LPS treatment in the iris- ciliary body and 48 hours after LPS treatment in the retina. The selective inhibition of E-selectin significantly blocked the cellular infiltration into the aqueous humor (P < 0.005) but had a milder effect on the protein concentration in the aqueous humor (P=0.0536). The inhibition of E-selectin and P-selectin almost abrogated cellular infiltration (P < 0.001). Myeloperoxidase activity in the retina 48 hours after LPS treatment was again significantly decreased by the inhibition of E-selectin alone and by the inhibition of E-selectin and P-selectin (P < 0.0001). A single injection of anti-E-selectin antibody 6, 12, or 24 hours after LPS injection effectively blocked cellular infiltration in the aqueous humor 24 and 48 hours after LPS treatment.

In EIU, E-selectin may be expressed on the vascular endothelium and remain after the period of expression of P-selectin and until approximately the time of maximum uveitis. The present results suggest that, in contrast to the role of P-selectin as an initiator of cellular infiltration, E-selectin may contribute to continuing cellular infiltration into the inflammatory site during inflammation, and its inhibition may contribute to the early resolution of the uveitis.